Drainage devices for removing fluids from the pleural cavity of a patient generally include a collection chamber, an underwater seal chamber and a liquid pressure control or regulating manometer which limits the negative pressure applied to the collection chamber. Fluid from the patient's pleural cavity is drawn into and accumulated in the collection chamber while gas and air from the pleural cavity are drawn through the liquid seal in the underwater seal chamber and into the source of suction. The liquid seal acts as a barrier to prevent the patient's pleural cavity from being exposed to atmospheric pressure and also prevents the patient's pleural cavity from being in direct flow communication with the source of suction. The background and operation of underwater drainage devices is discussed more fully in U.S. Pat. No. 4,439,190, issued to Protzmann et al on Mar. 27, 1984, which is incorporated herein by reference.
Under certain conditions, prior drainage devices have experienced the loss of their water seal due to sudden surges or even gradual increases in the negative pressure in the patient's pleural cavity. This may occur when the patient gasps for air or when the drainage unit is being used as part of an autotransfusion device. During the typical operation of an underwater drainage device, when the patient inspires, the liquid will move upwardly in the water seal column. As the patient expires, the negative pressure in the patient's pleural cavity decreases and the water moves downwardly in the water seal column. If the patient suddenly gasps for air such as when there is a blockage in the patient's bronchial tubes, the negative pressure in the patient's pleural cavity will dramatically increase. This sudden increase in negative pressure in the patient's pleural cavity will force the liquid in the water seal column to surge upwardly and, often times, the liquid will flow into the collection chamber, thus depleting the water seal.
Another cause for the loss of the water seal in the underwater drainage device may occur during a process known as autotransfusion. During autotransfusion, blood is suctioned from the patient's pleural cavity and stored in a collection bag attached to the side of and connected for suction to the suction inlet of the drainage device. When this blood is needed, the collection bag is attached to an I.V. and the stored blood is pumped back into the patient. As the blood is pumped back into the patient, the negative pressure in the patient's plerual cavity and the negative pressure in the collection chamber of the drainage unit will gradually increase. This increase in the negative pressure in the patient's pleural cavity causes the liquid in the water seal to be drawn upwardly into the water seal column. Once all of the liquid from the water seal is drawn upwardly into the water seal column, air will begin bubbling through the bottom of the column. As the bubbling occurs, liquid from the water seal passes into the collection chamber. Once the water seal is lost, the patient's pleural cavity will be in direct flow communication with the suction source and also to the atmospheric pressure as air from the atmosphere is drawn into the drainage device through the manometer chamber.
One approach to the problem of losing the water seal during sudden pressure changes is disclosed in U.S. Pat. No. 3,861,290, issued to Schachet on Jan. 21, 1975. The Schachet drainage device provides a secondary liquid seal incorporating a valve which permits a restricted flow of liquid during periods of high negative pressure from the patient's pleural cavity while permitting an unrestricted flow of liquid and gas in the opposite direction. Another approach is illustrated in the aforementioned Protzmann patent. The Protzmann patent discloses the use of a restrictive passageway consisting of a limited number of horizontally aligned baffles in the manifold.
Despite these and other underwater drainage devices which restrict the flow of the water seal, a need remains for an improved drainage device which will allow gas to flow through the water seal freely in both directions and will prevent the water seal from being lost or depleted during sudden or gradual changes in the negative pressure of the patient's pleural cavity.